2003 Ford Crown Victoria - Part 7, Ring and Pinion Gear Change

In our Oct. '11 issue, we added 70 hp to Project Panther using new cams and cylinder heads from Trick Flow. In the process, we raised the rpm where peak torque and horsepower occur. Since this is a heavy car (4,000 pounds) with a small (281ci) engine, we want to launch the car as close to the new torque peak as possible and help acceleration by increasing the torque multiple at the axle. Fortunately, Ford Racing has the best prices on 3.73:1 ring and pinion gear and bearing kits for the 8.8, so I ordered up a set and called Tech Editor Smith’s buddy Tim Moore, who agreed to do the install. While this is something I’d like to be able to do myself, I don’t have the collection of pullers, drivers, and presses, not to mention the wealth of knowledge and experience Moore has at his disposal. In some cases, it’s better to let a pro do the job, and I am not ashamed to admit this is one job I was willing to hand over to someone experienced. Though the job itself is a dirty one, the removal and replacement of the differential carrier is pretty straightforward. Installing the pinion gear at the right depth is where finesse and skill are required. Get it wrong and at best your final drive will howl like straight-cut gears; at worst, you can burn up the pinion gear bearings. Moore got it right, of course, and the result is a quiet-running pinion gear set and a more responsive car. Translation: It accelerates faster.

Hate all these Crown Victoria articles? That’s cool. Close your eyes and visualize this axle under your favorite Ford. The 8.8-inch came in nearly every FoMoCo rear-drive application for almost two decades. The job we’re showing here works across the board.

Determining Driveshaft Critical Speed

Here's the formula for determining driveshaft speed:

Road Speed x 336 x Rear Gear
__________________________
Tire Size

Checking my car running down the freeway:

75 x 336 x 3.73
____________ = 3,686 rpm driveshaft speed
25.5

This chart, provided by DynoTech Driveshafts, offers a guideline for safe driveshaft speeds. DynoTech General Manager Steve Raymond says operating above the critical speed and spinning faster than intended can cause the driveshaft to bend. As it bends, its overall length will shorten, causing it to pull out of the tailshaft of the transmission. In extreme cases, the driveshaft can even come apart, unspiraling like a paper towel roll. According to the formula, at freeway speeds, I’m well below the critical speed of my car’s 31⁄2-inch-diameter, 56-inch-long aluminum driveshaft (measured at the centerlines of the universal joints). However, on a recent trip to Willow Springs International Raceway, I reached speeds on the track of 100 mph, or 4,941 driveshaft rpm. Dynotech’s Raymond determined that my car can safely go about 144 mph. I doubt I have the horsepower to go that fast, but some readers’ cars might. If so, we recommend replacing the driveshaft with one that better matches the car’s operating conditions.